Fructose syrup (FS) such as high fructose corn syrup (HFCS) is commonly employed as a sweetener, in part since it is easier to handle than granulated sugar. Starch and table sugar (sucrose) represent the most common feedstocks for producing FS.
Processes for producing FS from starch begin by hydrolyzing this polymer to its monomer, glucose. The glucose is then treated with a glucose isomerase enzyme to convert the glucose to fructose, up to an approximately 50:50 mixture on a dry basis. The isomerization typically yields a syrup (“F42”) containing about 42% (dry weight basis [dwb]) fructose, at least about 50% (dwb) glucose, and a small fraction of oligosaccharides. The end point for the isomerization is selected to optimize the process economics. The fructose fraction of the F42 syrup is then enriched by chromatography to yield a syrup (“F90”) containing roughly 90% (dwb) fructose. The glucose-enriched fraction from the F42 syrup is recycled and further isomerized into fructose, which is then fractionated by chromatography to increase the overall amount of F90 syrup produced. F90 syrup is typically blended with F42 syrup to produce commercial sweeteners such as HFCS 55, which contains about 55% fructose (dwb), at least about 40% (dwb) glucose, and a small fraction of oligosaccharides.
Processes for producing FS from sucrose involve inverting this disaccharide to glucose and fructose using an immobilized invertase enzyme. The glucose and fructose are then fractionated by chromatography to yield a FS containing at least 90% (dwb) fructose. The glucose fraction is isomerized to F42 using an immobilized glucose isomerase and then further fractionated by chromatography to increase the overall amount of high purity fructose produced.
However, the chromatographic purification steps involved in producing FS from starch and sucrose feedstock are expensive and capital-intensive due to the large amount of evaporation required.
Other processes involving enzymatic approaches have been disclosed attempting to produce FS, but have fallen short in certain respects. U.S. Patent Appl. Publ. No. 2009/0123603, for example, appears to disclose using alternan sucrase to produce a syrup containing about 40% (dwb) fructose from sucrose feedstock. This low fructose level, coupled with the presence of soluble alternan polymer, would necessitate further processing in order to obtain a more useful FS. As additional examples, U.S. Pat. Nos. 8,828,689 and 8,962,282 disclose enzymatic production of fructose-comprising aqueous compositions. Such compositions, however, are not suitable for use in food applications given the presence of borate therein. Also, though U.S. Pat. No. 6,242,225 discloses enzymatic production of fructose, it is believed this process is limited to producing compositions with fructose and byproduct levels unsuitable for use as FS.
Thus, new processes for enzymatic production of FS are sought that require less processing steps and/or additives. To that end, disclosed herein is FS comprising at least 55% (dwb) fructose and production methods thereof employing a glucosyltransferase reaction.